1. Field of the Invention
The invention relates to a precipitated silica doped with alumina, a process for preparing a precipitated silica doped with alumina, and coating compositions comprising precipitated silica doped with alumina.
2. Discussion of the Background
Silicas and aluminum silicates may be prepared by precipitation from solutions of sodium silicate with sulfuric acid, or by precipitating solutions of sodium silicate by the addition of a soluble metal salt. In these known processes, salts or solutions of metal ions, for example, Zr, Ti, or Zn ions, may be added in a variety of ways. These ions may also bond with constituents of the silica/silicate surface to generate cationic charges on the surface of the silicas/silicates, and therefore may be not removed by simple washing. Such cationic silicas/silicates may be used, for example in coatings for ink jet papers to fix the anionic dyes typically employed in ink jet printing inks, and ensure bright colors in the paper coating.
In the paper industry, there is a need for fillers for media designed for ink jet printing which effectively absorb ink jet printing ink and maintain the brightness of the colors. In addition, rapid ink drying is vital to allow increased printing speed and to reduce the size of the printed dot. One way of meeting these requirements is to apply coatings containing silica to the media. These coatings permit rapid ink absorption, enhance the dot definition, and promote the defined circular propagation of the ink droplet. Furthermore, they prevent showthrough or strikethrough of the ink and produce high color densities.
Thus, in the paper industry, there is a need for fillers which are extremely easy to disperse, which when used in ink jet paper or inkjet film, for example, absorb the ink readily, and which maintain brightness of the ink colors.
Accordingly, it is an object of the present invention to provide aluminum-doped silicas in which the aluminum has been substantially embedded into the silicate structure.
It is second object of the present invention to provide a process for preparing aluminum-doped precipitated silica.
It is a third object of the present invention to provide a coating formulation comprising an aluminum-doped precipitated silica.